The present invention relates to a self-expandable stent with effective supporting ability, which can be compressed when it is delivered and can expand automatically after it is delivered.
"Stent" is known in the art as a prosthesis or graft used for reinforcing the blood vessel, such as an artery, or for maintaining patency of a hole, such as trachea and urinary esophagus, and the blood vessel after opening a stenosis in the artery. The stent has been effectively used in the vascular treatment in place of surgical exposing, incising, removing, replacing or bypassing a defected blood vessel required in the conventional vascular surgery.
The stent has a cylindrical shape, and functions to support a part of the patient's blood vessel or another anatomical lumen from the inside thereof so as to maintain the patency of the artery or to reinforce a dissected arterial wall or like, which may impede a fluid passageway by collapse thereof. According to the clinical data, it has been reported that occurrence of re-stenosis can be greatly reduced by using the stent after opening the stenosis by the balloon catheter.
There are many kinds of stents known already in the art, which are classified into various types. In these stents, there are a self-expandable type and a balloon expandable type.
In the balloon expandable type, the stent in a closed condition is mounted on a balloon catheter, and is delivered to a lesion or stenosis through the patient's meandering artery over a guide wire preliminary introduced in the artery. After delivery of the stent to a proper position, the stent is expanded by the balloon catheter.
In the self-expandable type of the stent, the stent in a closed condition is attached to a delivery catheter, and is delivered to a lesion or stenosis through the patient's artery, similar to the balloon expandable type. After delivery of the stent to a proper position, the stent is expanded automatically, which may be made by releasing a structure for allowing the stent in the closed condition, or other mechanism, such as using a memory alloy.
In any type, the stent should be flexible to be delivered through the narrow and meandering artery. Also, the stent in the installed condition should have enough strength to sufficiently support the dissected arterial wall or to keep opening stenosis. Therefore, the stent should be flexible, has a sufficient support structure, and can expand to a large size or diameter.
In the balloon expandable type, such as U.S. Pat. No. 5,135,536 and PCT Publication No. WO 94/17754, the stent is made flexible, and expandable to have a large diameter by inflating the balloon. Especially, when a wire is bent in a zigzag shape along the outer surface of the stent, as shown in U.S. Pat. No. 5,135,536, the stent becomes flexible. However, after the stent is expanded, the expanded stent is liable to shrink again, or is easily pushed back by the force of the blood vessel applied thereto.
In the self expandable type, such as U.S. Pat. No. 5,540,713, the stent made of a memory alloy has openings in a diamond shape in its open condition. When the stent is opened, the diamond shape frame can provide scuffling structure to sufficiently support the radial force. However, because of the diamond shape frame, the stent does not have flexibility in the longitudinal direction. Therefore, the stent can not be delivered to a narrow and meandering artery.
The present invention has been made in view of the conventional stents, and an object of the invention is to provide a self expandable type flexible stent which can be easily delivered through the meandering and narrow artery.
Another object of the invention is to provide the flexible stent as stated above, which can sufficiently expand in the radial direction by its own force, and can properly support a dissected artery.
A further object of the invention is to provide the flexible stent as stated above, wherein the size of the stent after enlargement is not substantially changed or reduced.
Further objects and advantages of the invention will be apparent from the following description of the invention.